Scenario 7 - Uplink Validation

Shift Turnover Notes

Date: Thursday, 0845 Local Station: Vermont (VT-01) Operator on Duty: You Supervisor: Charlie Brooks (off-site, main office) Shift Supervisor: Dana Torres (on-site, handling admin)

Overnight maintenance completed around 0300. HPA tube replacement and waveguide inspection - routine stuff. The transmit chain is powered down and needs validation before we resume normal operations.

Charlie’s stuck at the main office all day. Dana’s on shift handling paperwork. You’re expected to run this validation independently.

— Evening shift turnover

Charlie (phone call, 0830):

“Hey, it’s Charlie. Quick call - I’m stuck at the main office all day. Paperwork.

Overnight crew finished the HPA work. You need to validate the uplink before we go live. Standard post-maintenance procedure.

Dana’s on shift if you need anything, but you should be able to handle this. Mission Brief has the details.”

Active Services

Satellite	Customer	Service Type	Status
TIDEMARK-1	Teleport Services Inc.	Enterprise Data	Uplink offline (maintenance)

The transmit chain has been offline since midnight for scheduled maintenance. Customer traffic is routing through backup paths, but we need to restore VT-01 uplink capability before the morning traffic peak.

Maintenance Summary

Work Order: WO-2026-0127 Completed: 0300 Local Technician: Night maintenance crew

Work Performed:

HPA traveling wave tube replacement (scheduled)
Waveguide inspection and torque verification
BUC loopback test (maintenance verification)

Technician Notes:

“HPA swap complete, waveguide checks good. Ran loopback test to verify BUC output - signal looked clean. Powering down TX chain for day shift validation.”

TIDEMARK-1 Link Parameters

Frequency Allocation

Parameter	RF (MHz)	LO (MHz)	IF (MHz)
Beacon (Downlink)	4,175.5	5,250 (LNB)	1,074.5
Carrier (Downlink)	3,718	5,250 (LNB)	1,532
Carrier (Uplink)	5,943	7,000 (BUC)	1,057

IF Frequency Reference

Downlink (LNB LO above RF):

IF = LO - RF

Uplink (BUC LO above RF, lower sideband):

RF = LO - IF, so IF = LO - RF

Modem Configuration

Direction	Frequency (IF)	Bandwidth	Modulation	FEC	Power
Receive	1,532 MHz	36 MHz	QPSK	3/4	—
Transmit	1,057 MHz	36 MHz	QPSK	3/4	-7 dBm

Spectrum Analyzer Settings (Beacon Acquisition)

Parameter	Value	Notes
Center Frequency	1,074.5 MHz	TIDEMARK-1 beacon IF
Span	2 kHz	Narrow for CW beacon
RBW	Auto
Min / Max Amplitude	-100 / -30 dBm	Frames the beacon (about -49 dBm) with headroom

Station Reference

Vermont (VT-01) - Current State

Equipment	Status	Notes
GPSDO	Locked	Timing reference stable
Antenna	Program-track on TIDEMARK-1	Verified by night crew
LNB	Powered, reference locked	LO: 5,250 MHz
BUC	Check status	Maintenance may have left in test config
HPA	Disabled	Enable after validation complete
RX Modem	Configured	Should be operational
TX Modem	Verify config	Left on the crew’s narrow test carrier (950 MHz, 9 MHz, BPSK 1/2, -10 dBm)

Uplink Validation Sequence

Post-maintenance validation follows this sequence. Each phase builds on the previous.

Phase 1: System Health Check

Before touching RF equipment:

Check Dashboard for active alarms
Verify GPSDO locked
Note any fault conditions

Phase 2: Receive Chain Verification

Confirm the receive path is operational:

Antenna tracking TIDEMARK-1
LNB powered, reference locked, thermally stable
Beacon visible at 1,074.5 MHz IF (Span 2 kHz, Min Amp -100 dBm, Max Amp -30 dBm; it reads about -49 dBm)
Signal level nominal

Phase 3: Transmit Chain Configuration

Configure the TX modem for TIDEMARK-1 uplink:

Phase 4: Loopback Validation

Test the low-power TX chain before engaging the HPA:

Reduce BUC gain to 20 dB for loopback (keeps the LNB linear, see below)
Enable BUC loopback mode
Unmute BUC
Verify the loop carrier on the spectrum analyzer at 1,532 MHz IF (normal LNB LO, see below)
Confirm TX modem output is clean

Phase 5: Uplink Enable

After successful loopback validation:

Verify encryption status (AES-256 required)
Disable BUC loopback mode
Set BUC gain back to 23 dB (at 20 dB the HPA is 3 dB short of drive)
Enable HPA output
Adjust HPA backoff for required output power: above 400 W (TIDEMARK-1 link budget minimum). The HPA makes 60 dBm (1 kW) at P1dB, so 3 dB of back-off gives 57 dBm (501 W) and 4 dB gives 56 dBm (398 W, just short). Below 3 dB the overdrive alarm trips.
Verify uplink operational

The Ops Log records each power setting as you change it, for example “BUC gain set to 23 dB (was 20 dB)” and “HPA back-off set to 3 dB (was 10 dB)”, so the shift log can be read back from it.

Loopback Test Reference

Why Loopback First?

Loopback testing catches configuration errors before they cause interference. A misconfigured TX frequency or incorrect modulation settings are much easier to diagnose in loopback than by analyzing satellite return signals.

Where the Loop Carrier Appears

A C-band LNB only receives about 3.4-4.2 GHz, so it never sees the 6 GHz uplink directly and you do not retune it. The station’s test loop runs the coupled BUC sample through a loop translator that shifts it down by the satellite’s own translation frequency (2,225 MHz), so the loop carrier arrives where our downlink will be:

Stage	Frequency
TX modem IF	1,057 MHz
BUC output (7,000 - 1,057)	5,943 MHz
Loop translator (5,943 - 2,225)	3,718 MHz
LNB IF, normal LO 5,250 (5,250 - 3,718)	1,532 MHz

Leave the LNB LO at 5,250 MHz and look at 1,532 MHz IF (Span 50 MHz, Min / Max Amp -100 / -20 dBm, RBW Auto). The 36 MHz carrier sits in the same slot the RX modem watches for our downlink, so the loop also shows you what the receive side will see once the uplink is live. On RX Analysis a carrier this clean reads Effective C/N well under Raw C/N with ADC Status OPTIMAL: the grey ceiling line (about 40 dB) is the converter’s own limit, and Raw C/N combined with it gives the Effective figure. It is not a fault.

BUC Gain for Loopback

Mode	Recommended Gain	Reason
Normal TX	23 dB	About 16 dBm drive to the HPA from the -7 dBm modem, well under the BUC’s 28 dBm P1dB
Loopback Test	20 dB	Keeps the LNB linear (below)

The test loop (a directional coupler, a pad and the loop translator) feeds the BUC output into the LNB about 66 dB down. At 60 dB gain the LNB compresses at about -50 dBm in (its output P1dB is +10 dBm). At 23 dB the loop puts -50 dBm into it: 0.7 dB of compression and an “LNB input overload” alarm, so the carrier you measure is distorted by the test itself. At 20 dB it gets -53 dBm, 3 dB under, about 0.2 dB of compression: a clean, linear look at the modem and BUC. Put the gain back to 23 dB before the HPA goes on.

Encryption Requirements

Parameter	Required Value
Encryption Mode	AES-256
Key Status	Valid

Escalation Guidelines

Handle Yourself:

BUC configuration issues (mute state, loopback mode, gain)
TX modem frequency and parameter configuration
Loopback test execution
HPA enable sequence
Reference lock faults (power cycle usually resolves)

Inform Dana:

Equipment faults that don’t clear after troubleshooting
Unexpected alarm conditions
Validation complete (so she can update the shift log)

This is standard post-maintenance validation. Work methodically through each phase.

End of Briefing

The overnight crew did their part - the hardware is ready. Now you need to verify the configuration and bring the uplink back online.

Charlie’s not here to walk you through this one. Dana’s available if you need her, but she expects you to handle routine validation independently.

Work through the sequence: check for alarms, verify receive, configure transmit, test with loopback, then bring it live. Document any issues in the maintenance log.

When you’re done, VT-01 will be back at full capability and the customer traffic can route normally again.

Time to prove you’re ready.